Field of the Invention
The present invention relates to image sensors.
Description of the Background Art
Charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors have been used widely. Such an image sensor includes photodiodes serving as light receiving elements in pixels. When sensing incident light, each photodiode generates electric current. The photodiode accumulates electric current and then converts accumulated charge into voltage, so that a signal is derived from the corresponding pixel. The signals derived from all of the pixels are assembled into an image signal.
Such an image sensor has an exposure time that is the period over which the above-mentioned current is accumulated. This exposure time is controlled to be responsive to the intensity of light incident upon the photodiodes so that an appropriate image signal can be derived. If the exposure time is relatively long at a high luminous intensity, the amount of charge accumulated in the capacitor component would probably exceed the upper limit value, resulting in blown-out highlights. Thus, the exposure time at a high luminous intensity is shortened in order to avoid such blown-out highlights.
The techniques related to the present invention are listed below as Japanese Patent Application Laid-Open No. 2009-049459, U.S. Pat. Nos. 8,569,806, 8,610,234, 8,653,618, 8,669,598, and 8,669,599.